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    Compression Fatigue Behavior of Composites in the Presence of Delaminations

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    This paper discusses an experimental program that investigated the effect of imbedded (idealized) delaminations on the compression fatigue behavior of quasi-isotropic T300/5208 graphite/epoxy laminates. Three different stacking sequences of a 64-ply layup were tested. No lateral constraints were imposed on the specimen test section during static and fatigue loading, to permit unencumbered precipitation and propagation of delaminations. Test specimen geometry was chosen to preclude gross (Euler) buckling between test grip fixtures. Post-failure examination of specimen cross-sections revealed the absence of any fiber microbuckling. Consequently, the predominant failure mode in the test specimens was the propagation of imbedded delam-inations to the tab region. A 1-D delamination, located below the surface ply across the entire width, and a 2-D circular delamination, buried one or four plies below the surface, were considered. The out-of-plane deflection of the thin delaminated region was measured during static loading to estimate the extent of post-buckling that induces delamination growth. During fatigue, the growth of an imbedded delamination was monitored using diiodobutane (DIB)-enhanced radiography. A new procedure, involving laser-drilled minute holes, was used successfully in extending the application of enhanced radiography to buried delaminations. S-N, half-life residual strength, and ultimate strength data were obtained.


    interlaminar delamination, composites, graphite/epoxy, compression fatigue, enhanced radiography

    Author Information:

    Ramkumar, RL
    Engineering specialist, Structural Mechanics Research, Organization 3852/82, Northrop Corporation, Aircraft Division, Hawthorne, Calif.

    Committee/Subcommittee: E07.01

    DOI: 10.1520/STP34327S